Disposable absorbent articles such as feminine hygiene products are designed to absorb fluids from the wearer's body. Users of feminine hygiene products have several concerns. Leakage from products like catamenial pads, and in particular sanitary napkins, is a significant concern. The feel of the product against the wearer's body is also a concern. To provide better comfort, current sanitary napkin products are typically provided with a topsheet that is flexible, soft feeling, and non-irritating to the wearer's skin. The topsheet does not itself hold the discharged fluid. Instead, the topsheet is fluid-permeable to allow the fluids to flow into an absorbent core.
Over the years, topsheets have improved to provide a cleaner, drier, and more comfortable in-use experience. In some feminine hygiene products, the topsheet is made of a hydrophobic material. These materials can include phobic nonwovens, hi-loft nonwovens, and softer films with significant texture (micro apertures, nubs that can trap fluid within the film structure etc.), and can be manufactured from a wide range of materials such as apertured plastic films, natural fibers (e.g., wood or cotton fibers), synthetic fibers (e.g., polyester or polypropylene fibers) or from a combination of natural and synthetic fibers. The hydrophobic nature of these materials helps to isolate the wearer's skin from liquids absorbed by the product and thus improves comfort by reducing the phenomenon known as “rewet”.
Absorbent cores are well known in the art, and have conventionally included tangled masses of fibers, i.e., fibrous webs that can imbibe fluids both by an absorption mechanism (in which fluid is taken up by the fiber material itself) and by a wicking mechanism (in which fluid is acquired by, distributed through, and stored in capillary interstices between fibers).
Although the properties of a hydrophobic nonwoven topsheet helps to keep fluids in the core, the tendency of such topsheets to repel fluid creates a risk that the fluid will flow off the topsheet, rather than flow through the topsheet and into the absorbent core. This challenge is particularly evident in connection with feminine hygiene products, which commonly encounter fluid flow rates of less than 1-3 grams per hour, rather than the gushing flow rates commonly encountered by incontinence products. For fluid to flow into a feminine hygiene product, it must overcome not only the hydrophobic properties of the topsheet, but also the natural adhesion of the fluid to bodily surfaces.
To help ensure that fluids flow into the absorbent core, some feminine hygiene products with hydrophobic topsheets are constructed with what is sometimes referred to as a secondary topsheet (STS) directly beneath the topsheet. This secondary topsheet is designed to acquire the fluid on a liquid-permeable topsheet and distribute it to the underlying absorbent core. To help ensure that the secondary topsheet transfers the fluid to the absorbent core, secondary topsheets typically have sufficient capillarity to draw the fluid through the topsheet. To ensure that the fluid flow continues onto the absorbent core, the secondary topsheet is commonly designed with more permeability than the absorbent core, and less capillarity than the absorbent core.
Secondary topsheets are typically made from an airlaid-tissue web made from hydrophilic cellulosic fibers, sometimes referred to as an airlaid STS. Such secondary topsheets, however, cannot be fusion bonded to the topsheet due to the use of plain cellulosic fibers in the web. Accordingly, glue is used during the manufacturing process as a bonding agent between the airlaid STS and the topsheet. If fusion bonding is desired, a polyethylene (PE) powder can be incorporated into the airlaid STS, but a sufficiently high basis weight is required, which may be undesirable.
Accordingly, it would be desirable to provide a fibrous web for use as a secondary topsheet, with the fibrous web having a relatively lower basis weight, while still having a sufficient flexural rigidity and desired fluid handling and performance characteristics.